Wrack mostly consists of the kelp that washes onto beaches from the ocean. Wrack is an essential part of the ecology of the shoreline, providing food and habitat for everything from insects to birds.
Figure App.F.13.8.. A figure showing the averaage density of two important sandy beach-dwelling invertebrates (shown in red and blue) from eight surveyed beaches on Santa Rosa Island from 1994 - 2015.

Figure App.F.13.8.. A figure showing the averaage density of two important sandy beach-dwelling invertebrates (shown in red and blue) from eight surveyed beaches on Santa Rosa Island from 1994 - 2015.

Click for Details Mean density of two important members of the upper beach macrofaunal community — California beach hopper Megalorchestia californiana (red) and Alloniscus perconvexus (blue )— from surveys of eight beaches on Santa Rosa Island from 1994–2015. Curved lines represent statistically smoothed means. Figure: Channel Islands National Park